But her comments, which have included a warning that Mr Corbyn's leadership is only helping the Conservatives, have won praise from Frank Field, the prominent chairman of the work and pensions committee.

Mr Field has written to the author to tell her he believes she "hit the nail on the head".

"It is remarkable he has got half a million new members," the MP for Birkenhead said in the letter.

"If he could spell out how this becomes a social movement, rather than an execution squad of Labour MPs, and ties in with what political parties do to try and win elections, then we will be a step forward.

"I failed to get him to do any of this I'm afraid.

"So well done for your blast of reality."

Rowling has long been a prominent supporter of Labour, giving the party £1 million under the leadership of Gordon Brown.

She recently offered her backing to the Saving Labour campaign to replace Mr Corbyn.

She described Mr Corbyn as a "lousy leader" as she responded to criticism of her remarks on Thursday.

She tweeted: "If you've got to be a millionaire to think Corbyn is a lousy leader, most of this country is secretly loaded."

The Twitter storm was kicked off by a message posted by Rowling - following a poll giving Mr Corbyn a 24-point lead over Mr Smith - in which she wrote: "One day in the far distant future we'll look back and we won't laugh, Labour. Because this isn't bloody funny."